Blastocystis hominis, a protozian parasite of the human gastrointestinal tract and an organism implicated in the causation of human diarrhea, is being studied in terms of its morphology, physiology, and sensitivity to metronidazole, enterovioform and similar drugs. This sporozoan may contain hundreds of mitochondria, although it is a strict anaerobe. Whether these are anaerobic mitochondria, and their enzyme activity, if any, are subjects of the study. Mean generation time of B. hominis is from 5-10 hours. B. hominis is sensitive to metronidazole, enterovioform, and other oxyquinoline derivatives. Cell division of B. hominis is commonly asexual, with sexual reproduction occurring rarely.